Fraunhofer project utilises ultrasound to produce stronger AM parts

November 17, 2022

Experimental set-up for ultrasound-assisted laser-directed energy deposition (Courtesy Fraunhofer IWS Dresden)
Experimental set-up for ultrasound-assisted laser-directed energy deposition (Courtesy Fraunhofer IWS Dresden)

The Fraunhofer Institute for Material and Beam Technology IWS Dresden; the Fraunhofer Additive Production Technologies Facility IAPT, Hamburg, Germany; and the RMIT Centre for Additive Manufacturing, Melbourne, Australia, have begun a €4 million UltraGrain project with a meeting on “On-demand grading of grain structure by ultrasound-assisted AM – from demonstration to industrialisation.”

“This joint project with RMIT and Fraunhofer IAPT holds a special place in our hearts,” stated Professor Christoph Leyens, Executive Director of Fraunhofer IWS and Adjunct Professor at RMIT.

Professor Ingomar Kelbassa, Executive Director of Fraunhofer IAPT and also Adjunct Professor at RMIT, added, “Both Fraunhofer IAPT and Fraunhofer IWS have been cooperating with the Australian colleagues for a long time through personal contacts. UltraGrain, however, is the first project to receive funding that will lead directly to the transfer of joint research results into industrial practice.”

Considering the deepened cooperation, the Fraunhofer-Gesellschaft is funding the project with €1.5 million from its International Cooperation and Networking ICON programme. The Australian partners are contributing a further €2.5 million euros.

The RMIT Centre for Additive Manufacturing project collaborators Associate Prof Andrey Molotnikov, Distinguished Prof Milan Brandt and Distinguished Prof Ma Qian are reportedly optimistic about the application of ultrasound to microstructure manipulation. They are reportedly convinced that the next generation of aerospace, as well as space part Additive Manufacturing, will significantly benefit from the uptake of the ultrasound technology which will be co-developed with the Fraunhofer partners.

In the process, the researchers are entering new technological territory. With the aim of specifically influencing the internal grain structure of AM components and, thus, their mechanical properties, researchers are combining the established wire- and powder-based Directed Energy Deposition (DED) processes with ultrasound, which vibrates beyond the tones audible to humans. During the deposition process, the ultrasound sends fine vibrations with a precisely defined frequency globally through the resulting component or locally following the laser and directly to the melt pool, for example. The ultrasound prevents undesired columnar structures from forming in it – and these microscopic columns result in poorer mechanical performance. However, under ultrasonic action finer, round shaped micrograins are formed, being almost evenly distributed or graded and weakening the undesired texture.

This equiaxial alignment increases the mechanical and chemical load-bearing capacity of the additively produced work pieces among others. Because the ultrasound can be controlled in a targeted manner, component designers are able to specify exactly where the work piece will be subjected to great stresses later in use. There, the developers can plan for an ultrasound-controlled grain structure, but also decide at which points they can do without it in favour of faster production. Such grading is essential if, for instance, gas tanks for space probes have to endure the special challenges of outer space for years to come, or if tools in car factories have to resist even high point loads in mass production.

“With UltraGrain, we can significantly improve the properties like fatigue resistance, strength, toughness and ductility or reduce the cracking susceptibility of additively manufactured components,” stated Dr Elena López, project leader from the Fraunhofer IWS. “In addition, this project opens up the opportunity to establish new contacts in Australian industry and increase the international revenues of our institute.”

Fraunhofer IWS is contributing its experiences in laser cladding to the research alliance. In particular, emphasis will be placed on AM processes involving equipment that feeds the desired titanium or steel alloys to the laser in wire form. Investigations with powder-based starting materials are also planned.

Fraunhofer IAPT deals with the optimal design of components with different grain structures. In the sense of a multi-material design, the scientists intend to develop a methodology for the optimal placement of ultrasonically influenced material areas. Furthermore, Fraunhofer IAPT is concerned with optimal path planning for the new process technology.

As international university partner in UltraGrain, RMIT Centre for Additive Manufacturing will explore the physical processes that ultrasound triggers in the material during the new process approach using advanced synchrotron measurements. The Australian team will also investigate possible scaling effects. During the transition from pure laboratory production of centimetre-sized components to additively produced series components that span several decimeters or even meters, unexpected side effects may quite possibly occur.

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